The present invention relates generally to novel fluoropolymers, and more specifically, to fluoropolymers, methods of making and articles manufactured therefrom, which fluoropolymers have been permanently modified at the molecular level but without altering the materials original surface morphologies as well as bulk characteristics.
Fluorinated polymers, such as fluorohydrocarbon polymers, e.g., polyvinylidene fluoride, polyvinyl fluoride (PVF), including the well-known fluorocarbon polymers, e.g., perfluorinated materials, such as PTFE, are characterized by extreme inertness, high thermal stability, hydrophobicity, and a low coefficient of friction as to resist adhesion to almost any material. While these properties are highly desirable, it would also be advantageous to modify some of the polymers' characteristics in order to expand the scope of their useful applications. For instance, in the field of biocompatible materials fluorocarbon polymers in various forms have been developed, but because of their chemical inertness and extremely low reactivity the scope of these improved devices, such as implantable prosthetic devices and probes has been limited. In the field of membranes and filters, fluoropolymers have also had limited applications due to low surface energy problems associated with these materials. Membranes and filters fabricated from PTFE, for example, are unable to selectively inhibit permeation of liquids with high surface tensions (&gt;50 dynes/cm) while allowing liquids having lower surface tensions to pass through. PTFE has also been under intense study for applications in cell culture growth membranes, but a principal shortcoming has been the inability of cells to adhere to this low energy material.
Efforts of others to modify the properties of fluoropolymers have not been totally satisfactory. U.S. Pat. No. 4,548,867 (Ueno et al), for example, discloses a fluorine-containing synthetic resin having improved surface properties as evidenced by increased wettability with water, printability and susceptibility to adhesive bonding. The fluoropolymer is exposed to a low temperature plasma comprising an organic nitrogen-containing gas. Instead of modifying the atomic composition of the fluoropolymer starting material, Ueno et al form a thin "layer" of a nitrogen-containing wettable material thereto. Consequently, the adherence of such an overcoating tends to alter the microstructural morphology of the original polymer, especially with respect to pore size. This coating also alters desirable surface properties exhibited by the original fluorinated material.
Others have attempted the use of glow discharge and corona treatments to produce surface modifications. In some early work, Schonhorn and Hansen found that exposure of polyolefins and perfluorinated polymers to low power radio frequency electrodeless discharges in inert gas atmospheres produced favorable results over wet chemical methods. Their improvement in the bondability of surfaces was limited and attributed to the formation of a highly cross-linked surface layer. Studies of Hollahan et al, J. Polym. Sci., 13, 807 (1969) aimed at rendering polymer surfaces biocompatible included the interaction of PTFE with plasmas excited in ammonia and nitrogen/hydrogen mixtures, the goal being the introduction of amino groups into the polymer surface. However, the long exposure times and high powers employed provided only limited results, and further, are thought to have produced significant changes not only in the surface chemistry, but also the native bulk properties. Morphology of the surface was also severely effected.
In another ESCA study entitled "ESCA Study of Polymer Surfaces Treated by Plasma," Yasuda et al, J. Polym. Sci., Polym. Chem. Ed., 15, 991 (1977) the effects of discharges in argon and nitrogen on surface chemistry were considered on a range of polymers. PTFE was found to be particularly susceptible to defluorination and the introduction of oxygen and nitrogen moieties into the surface. Accordingly, there is need for permanently modified fluorinated polymers in which some of the original fluorine functionality is eliminated and replaced with oxygen functionality and hydrogen bonded to the carbon polymer backbone without the formation of coatings or layers while substantially preserving the original surface morphology and bulk characteristics of the unmodified material on a molecular scale.